This invention relates generally to heat exchangers, and more particularly to a cylindrical heat exchanger member designed to be used: in, for example, a commercial boiler/water heater. Boilers/water heaters in general are well known in the art, as are cylindrical heat exchanger members. In the context of heat exchangers, the term xe2x80x9ccylindricalxe2x80x9d denotes the general overall shape of the heat exchanger member.
Early heat exchanger members have been configured from straight tubular members arranged in adjacent rows, forming a generally xe2x80x9cflatxe2x80x9d rectangular member. Water, typically, is circulated through the tubular members where it is heated, such as by a burner located inclose proximity to the tubular members. The heated water is then circulated downstream for use elsewhere in the heating system. As requirements for heating capacity increased, cylindrical shaped heat exchanger members were created to increase the firing density of the boiler. Firing density is generally defined as the output in British Thermal Units (xe2x80x9cBTUsxe2x80x9d) divided by the combustion chamber volume. Operating the burner at a higher temperature can provide an increase in firing density since the BTU output can be increased without reducing combustion chamber volume. However, an off-setting consideration is the effect of combustion chamber volume on emissions. In particular, emissions, or waste products, such as CO and NOx, generally increase as-a result of operating the burner at a higher temperature for a given volume combustion chamber. There is also another important factor which must be considered in regard to the relationship between BTU output and combustion chamber volume. This factor is the effective surface area of the heat exchanger member. Generally, the larger the surface area of the heat exchanger member, the higher the BTU output that can be achieved for a given combustion chamber volume and burner temperature. Consequently, it can be understood that the firing density of a boiler can be increased while maintaining a proper combustion chamber volume by designing a heat exchanger member with the largest possible surface area and the smallest overall size.
In the prior art, firing density has been increased using a heat exchanger member configured by arranging straight tubular members in a circular pattern to form a cylindrical shaped member. In this manner, the overall volume of the heat exchanger member is reduced while maintaining surface area, thus increasing the firing density for a given combustion chamber volume. To circulate and control the flow of the water through the multiple straight tubes, a header is connected at both the top and the bottom ends of the straight tubes to control flow through each tube. One of the two headers commonly has both the inlet and outlet connections for circulating the water through the straight tubular members. The headers can be conifigured internally to provide desired flow paths through the tubular members.
In addition to straight tube cylindrical heat exchanger members, it is also known in the prior art to use one or more single hollow tubular members which are wound in a spiral configuration to create a compact, generally cylindrical shaped heat exchanger member. However, like straight tubular members, each end of the spiral shaped tubular members must communicate with a header for circulating water therethrough. The water circulated through the. tubular members is heated by a burner, which, for reasons of compactness, is typically disposed concentrically within the cylindrical shaped heat exchanger member. After being heated, the water is circulated from the boiler for utilization elsewhere in the heating system.
One disadvantage of conventional cylindrical heat exchangers members using straight tubes, such as described above, is a less efficient ratio of surface area to combustion chamber volume. Another disadvantage is that the flow path of the water through the tubular members cannot be readily reconfigured from the original configuration, in large part due to the use of two separate headers. In fact, new headers would likely have to be made to change the flow path. Moreover, if the boiler size drops, the length of the straight tubes is shortened. However, the bulk water flow cannot be reduced because the number of tubes is the same, and therefore smaller, less expensive pumps cannot be used even though the boiler size is smaller. Also, cleaning the insides of the tubular members is difficult because each end of the multiple tubular members in prior art type heat exchanger members is connected to a separate header at opposite ends of the tubes. Furthermore, the conventional cylindrical heat exchanger members with top and bottom headers generally are not very effective at keeping debris and scale from collecting in the bottom header.
Accordingly, there is a need for a cylindrical shaped heat exchanger member which can provide a large surface area in a compact package in order to increase the firing density of the boiler, while maintaining a proper combustion chamber volume so that emissions are reduced. Furthermore, there is a need for such a cylindrical heat exchanger which also provides for easily cleaning the hollow tubular members and enables convenient reconfiguration of the flow path of the water through the hollow tubular members.
A cylindrical heat exchanger member of a heating boiler/water heater is provided wherein the cylindrical heat exchanger member is formed of multiple stacked tubular rings. Water, the typical heating medium, is circulated through the stacked tubular rings and heated by a burner disposed generaly concentrically within the stacked tubular rings. Each end of each of the multiple stacked tubular rings can be terminated at a single longitudinally extending header which intersects each tubular ring. The header can have inlet and out let connections for circulating water from a Water source through the tubular rings and out therefrom for use elsewhere in the heating system. A water barrier can be positioned within the header, and can be interchangeable, to provide easily reconfigured control of the flow path of the water through the cylindrical heat exchanger member. The number of stacked tubular rings can easily be varied, and more than one row can be provided, such that nested stacks of tubular rings can be used to form a dual row cylindrical heat exchanger member. Also, the number of rings can be reduced if the size of the boiler reduced, permitting a lower bulk water flow and thus use of a smaller less expensive pump. The single header also enables efficient cleaning of the inside of each tubular ring due to easy access to each end of each tubular ring at a single location. Moreover, the tubular ring design is more effective getting debris and scale swept out of the headers because the water flow keeps the debris and scale agitated so it is more easily swept out.
The boiler in which the cylindrical heat exchanger member is utilized can be similar to conventional boilers, in that the cylindrical heat exchanger member can be enclosed in a housing portion connected to an air/gas delivery system. The air/gas delivery system can include a blower and a burmer, which is typically disposed generally concentrically within the stacked tubular rings. The air/gas delivery system can be connected to a gas train which supplies fuel to the burner, and a flue transition member can be provided next to or as part of the housing portion for exhausting combustion products created by the burner. Water is circulated through the tubular rings where it is heated by the burner, and thereafter is circulated downstream of the boiler for utilization elsewhere in the heating system.